The Clinical Studies Section provides the clinical Epidemiology Branch with a large patient resource for bedside studies of cancer etiology. In the last 3 years, over 400 questionnaire interviews of childhood cancer patients have been completed, and an analysis of findings is in progress. Through the interviews, several unusual family aggregates of cancer have been identified for more detailed clinical and laboratory studies. Additional familial clusters of cancer, including childhood cancer in 38 sets of siblings, have been identified through retrospective review of hospital records at several Boston medical centers. A Registry of Survivors of Childhood Cancer has been set up through collaboration of the Clinical Studies Section and the Sidney Farber Cancer Center. The 500 registrants represent approximately 2% of all survivors of childhood cancer in the last 2 decades. Patients in the series are being observed for second malignancies, cancer in close relatives, and genetic effects in progeny. In a new study, the unusually high mortality of bladder cancer in Vermont, and of lung cancer in selected Maine counties are being investigated through an analysis of death certificates.